Incidentally discovered asymptomatic extramedullary plasmacytoma involving the orbit and dura

Extramedullary plasmacytoma of the orbit is rare and usually occurs with multiple myeloma. We report an incidentally discovered asymptomatic orbital and dural plasmacytoma in a 71-year-old man evaluated after a fall. Magnetic resonance imaging demonstrated diffuse enlargement and enhancement of the left extraocular muscles, optic nerve sheath complex, lacrimal gland, cavernous sinus, and pachymeninges. Serum studies identified an IgG-kappa monoclonal gammopathy, and dural biopsy revealed a kappa-restricted CD138-positive plasma-cell neoplasm. Systemic staging showed no myeloma-defining end-organ damage or additional lesions, although bone marrow biopsy showed 8% to 10% clonal plasma cells, favoring solitary extramedullary plasmacytoma with minimal marrow involvement rather than overt multiple myeloma. The patient received external-beam radiotherapy to the orbit and involved dura (45 Gy) with marked radiographic improvement. At 1 year, he retained 20/20 vision, full extraocular motility, and no evidence of progression. This case highlights that even extensive orbital plasmacytoma may remain clinically silent and that prompt biopsy, staging, and radiotherapy can preserve excellent function.